Servers, computers, and other systems that require high data rate communication channels have employed optical signals for communication among subsystems and circuit boards. Optical signals have the advantage of avoiding the signal loss resulting from the impedance inherent when transmitting high frequency electrical signals on conductive lines. In particular, with data rates on the order of one Gbit/second or more, transmission of electrical signals on conductive lines more than a few centimeters in length can result in significant signal loss and noise.
Many systems and devices for transmission and conversion of optical signals on or between printed circuit boards have been developed. One solution for optical signaling employs hollow core waveguides. Hollow core waveguides, which are sometimes referred to as hollow metal waveguides or light pipes, have walls lined with a reflective coating such as one or more layers of metal, dielectrics, or other materials that make the walls suitably reflective. The reflective walls surround a hollow core or air channel in which a light beam can propagate. Hollow core waveguides can provide advantages in many systems. For example, a light beam transmitted through a hollow core waveguide can often be guided around sharper bends than are possible with some other waveguides or optical fibers that rely on total internal reflection. Also, the cross-section of a hollow core waveguide can also be large relative to the wavelength of the light guided, so that a hollow core waveguide can guide light beams with relatively large beam widths. Hollow core waveguides further allow transition between guided and free space propagation of light without an air-solid interface at which optical power can be lost. For data transmissions at higher data rates, new systems and methods for transmission and conversion of optical signals will be needed, and systems and methods that work with hollow core waveguides may be desired.
Use of the same reference symbols in different figures indicates similar or identical items.